Spark arresting structure for a muffler having a catalytic converter

ABSTRACT

Muffler with catalytic converter (1) essentially arranged in direct connection with a combustion engine&#39;s exhaust port and mainly intended for portable working tools such as chain saws. A spark arrester screen (3), i.e. a structure (3) which at least partly contains a wire mesh (4) and a net (4), usually made of metallic material, is located in the exhaust gas flow downstream a converter element (5). In connection with the spark arrester screen (3), upstream or downstream the screen, flow dividers (8, 13, 9) are arranged.

TECHNICAL FIELD

The subject invention refers to a muffler with catalytic converterarranged basically in direct proximity to an exhaust port of acombustion engine and mainly intended for portable power equipment suchas chain saws.

BACKGROUND OF THE INVENTION

For portable power equipment such as chain saws, mufflers have sincelong in some cases been equipped with so called spark arresters. Thisarrester was then often positioned at the outlet of the muffler with thefunction to trap any sparks so that these did not exit the muffler. Fora two-stroke engine chain saw for instance, the exhaust gases have atemperature of approximately 600 degrees C. when entering such a sparkarrester screen. The mesh is commonly made of stainless acid proofmaterial in order to stand such high thermal loads.

Small combustion engines have since long had comparatively high exhaustemission levels. This particularly applies to two-stroke type engines,because the combustion is more incomplete than in the case offour-stroke engines. Increased demands concerning exhaust emissions fromsmall engines have however resulted in the introduction of catalyticconverters for different types of small engines. This also applies tosmall engines for portable equipment such as chain saws etc.. Severaldifferent solutions for so called catalyst mufflers, particularly forchain saws, have emerged. These mufflers are usually connected directlyto the exhaust port of the cylinder. A catalytic element is placedinside the muffler, and in the element an exotherm chemical reactiontakes place. For chain saws for instance, this implies a temperatureincrease inside the muffler from around 600 degrees C. before thecatalytic element to around 1000 degrees C. after the catalytic element.The applicant does not know of any case where a muffler with a catalyticconverter has been equipped with a spark arrester positioned in theexhaust flow downstream the catalyst element. Due to the high exhaustgas temperature after the element, the working conditions for such aspark arrester become very difficult. At the same time, it is in manycases preferable to position a spark arrester downstream the catalyticelement in order to reduce risks for fire and accidents when using thepower equipment.

The muffler with catalytic converter in accordance with the inventionthus is essentially characterized in that a spark arrester, i.e. astructure that at least partly contains a wire mesh or a screen, usuallymade of metallic material, is positioned in the exhaust flow downstreama catalytic element. Furthermore the spark arrester screen is usuallypositioned in close proximity to the exhaust outlet. In order towithstand the high thermal loads on the spark arrester screen, so that areasonable life time can be obtained, a number of different measures areused, on their own or in combination with each other. Partly designmeasures on the spark arrester screen itself to achieve a welldistributed heating of the screen and good cooling, e.g. measures forseparation of the exhaust flow. Partly restriction are use in themuffler upstream to achieve increased turbulence in the exhaust streamand thereby cause better distribution across the spark arrester screenand at the same time achieve better cooling of the exhaust stream beforeit reaches the spark arrester screen. These and other characteristicsand advantages will be apparent from the ensuing description of thepreferred embodiments and with the support of the drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in closer detail in the following by wayof various embodiments thereof with reference to the accompanyingdrawing figures.

FIG. 1 shows in perspective a catalytic muffler with spark arresterscreen according to the invention. Most parts are shown in an explodedview-manner to make the construction and functioning more clear.

FIG. 2 shows a cut away side view of a type of spark arrester screenattached to a catalytic muffler according to FIG. 1 or a similarcatalytic muffler.

FIG. 3 shows the spark arrester screen according to FIG. 2 from abovefor clarity the cooling air conductor 48 has been removed.

FIG. 4 shows a cut away side view of another embodiment of the sparkarrester screen.

FIG. 5 shows the spark arrester screen according to FIG. 4 from above.

FIG. 6 shows a cut away side view of a further embodiment of the sparkarrester screen.

FIG. 7 shows a cut away side view of yet another embodiment of the sparkarrester screen.

FIG. 8 shows the spark arrester screen according to FIG. 7 from above.

DESCRIPTION OF EMBODIMENTS

In FIG. 1 numeral reference 1 designates a catalytic muffler accordingto the invention. It is usually composed of two mutually detachable mainparts. a muffler 42 and a lid 43, which seals the muffler housing. Abaffle 53 with a number of restriction holes 51 can be positionedbetween the muffler housing 42 and the lid 43, or it can form part of amore complex lid 50. A catalytic element 5 is positioned in the lid 43and from this element 5 an exhaust duct 45 comes out of the muffler. Theexhaust duct 45 is entirely positioned in the lid, so that the exhaustgases are emitted via the lid. The lid is composed of several componentsjoined together, which are here shown in an exploded view. The lid isconsequently constructed of an inner plate 12, an outer plate 13 and acooling air conductor 48. The catalytic element 5 is positioned betweenthe inner plate and outer plate 12 and 13 respectively. It is simplyclamped between these two plates. The tree plates 12, 13 and 48 aresuitably spot welded together to form lid 43. However, they can also bejoined together in other ways.

The catalytic muffler 1 is mounted to the cylinder of the engine. Thisis achieved by fastening the muffler housing 42 to the exhaust port ofthe engine with screws inserted in holes 26, 27 and 33. The aperture 25in the muffler housing 42 corresponds to the exhaust port. On theopposite side of the muffler housing 42 there is a large opening, whichfacilitates fastening screws through the holes 26, 27 and 33. Exhaustgases 21 from the exhaust port exits into the muffler housing 42. Theside of the muffler housing that is hidden in the figure and turn awayfrom the exhaust port aperture 25 is supplied with a fastening plane forthe lid 43. This fastening plane has four tapped holes corresponding tothe holes 28, 29, 30 and 31. The fastening plane has as mentioned alarge opening. Depressions in the inner plate 12 intended for theconverter element 5 and the exhaust gas duct 45 protrude into thisopening. A gasket 24 is positioned between the lid 43 and the mufflerhousing 42. For clarity the figure shows a part of the gasket 24positioned on the inner plate 12. When the baffle 53 is used, it issuitable positioned against the inner plate 12 and spot welded togetherwith the plates 12, 13 and 48 to form a lid 50. The gasket 24 is thenpositioned on the inside of this lid, i.e. on the baffle 53.

The exhaust gases 21 from the exhaust port of the engine therefore flowsout into the muffler housing 42, which, in the first mentioned case, issealed by the lid 43, except for an aperture 20.The exhaust gases flowin through the aperture 20 and through the converter element 5, which isfixed between the inner plate 12 and the outer plate 13. When the baffle53 is used, the exhaust gases initially flow through the holes 51 andthen through the aperture 20. The converter element is usually composedof at least one strip, normally made of metal, with corrugations orsimilar, coated with a catalyzing layer. The strip is rolled or foldedaround a longitudinal axis 46 and the converter element is so positionedthat this longitudinal axis 46 is essentially parallel to the crankshaft47. In this case the converter element consists of two strips rolledtogether, one corrugated and one flat, and the strips have been rolledtogether into a cylindrical element. This is clamped betweenpart-cylindrical depressions in the inner and outer plate, 12 and 13respectively. Also other types of converter elements can be used, e.g.ceramic.

After the exhaust gases 21 have passed through the converter element 5,where they have been cleaned, they proceed in an exhaust gas duct 45,which is integrated in the lid 43, and are then further conducted to anoutlet 16. The outlet 16 can consist of stamped apertures in the plate13. The outlet is equipped with a spark arrester screen 3, whosefunction is to catch sparks in order to prevent them blowing out of themuffler. The screen 3 is suitably positioned to cover the outlet 16 andbetween the plates 12 and 13, but other positions are also possible. Theexhaust gas outlet 16 has here been designed in the form of so calledgills. The aperture in each of these gills is turned in the oppositedirection compared to the direction of the exhaust gas flow. Thus thedirection of the exhaust gas flow is turned in the gills 16. At thegills the exhaust flow changes its direction 180 degrees. This isimportant since a cooling air guide plate 48 is positioned on theoutside of the outer plate 13 and the cooling air guide plate directscooling air for mixing with the exhaust gases and for cooling theconverter element.

The cooling air guide plate 48 is as mentioned positioned in anouter-most position on the lid 3 and it consists of an outer guide plate49, which collects and directs cooling air 10 from the cooling fan ofthe engine between itself and parts of the lid positioned inside it, anda number of abutments 11 which attach the guide plate 49 to inner lidparts by means of e.g. screws and/or welding. The guide plates 49 has anupstream edge 32, and after the cooling air guide plate 48 has beenassembled to the other lid parts the upstream edge 32 will be situatedwell outside the side of the plates 12 and 13. When all three plateshave been joined together, e.g. by spot welding the holes 29, 29' and29" will be in correspondence with each other as well as the holes 28,28' and 28", where`--designations have been used for holes in the outerplates 13 and "--designations for holes in the cooling air guide plate48. For holes in the partition walls 53 "--designations have been used.The upstream edge 32 of the outer guide plate 9 is directed almostparallel with the side of the muffler housing 2. Downstream the outerguide plate turns almost through 90 degrees and thus the cooling air 10is guided in parallel with the outside of the outer plate 13. Thecooling air 10 will thus mix with the hot exhaust gases 21 so that themixed will be at a lower temperature. The cooling air 10 will also sweepover a bulge 19 in the plate 13, the converter element 4 being housed onthe inside of the bulge. As the converter element will be very hot thiscooling is of great significance.

In this case the outer guide plate 9 of the cooling air guide plate 8 isdrawn down towards the outer plate 13 to create a centerfin 18. Thiscenterfin divides the flow of cooling air 10 into one part that runsover the exit 16 and one part that runs over the back side 19 of thehousing of the converter element. Thus it is assured that the coolingair is not unevenly distributed between these two important coolingobjects.

As is evident from the figure the lid 43 consists of, apart from thecooling air guide plate 48 and the converter element 5, essentially twoplates 12, 13. An inner plate 12 and an outer plate 13 and at least oneof the inner plate 12 and the outer plate 13 has a depression turnedaway from the other plate 12, 13, so that therefore the converterelement and the exhaust gas duct 45 can be housed between the platesafter these have been joined together. In the shown embodiment thecylindrical converter element 5 has been placed between depressions inboth the inner plate 12 and the outer plate 13. The depression in theinner plate 12 is bigger than the depression in the outer plate 13. Thisis desirable because the whole aperture 20 must be located in the innerplate 12. The exhaust gas pipe 45 is however in this case formedentirely as a depression in the inner plate 12, the outer plate 13remaining essentially flat. There is even a local bulge 33 in the outerplate 13, and this bulge is located just in front of the exit 16. Thiscreates a local throttling and a certain change of the direction of flowtowards the outlet 16 that is desirable.

A throttling 15 can be made in the exhaust gas pipe 45 and locatedbetween the converter element 5 and the exhaust gas outlet 16 out of thelid, in this case this throttling is formed as a throttling washer 15fixed between the inner and outer plates 12, 13 and located immediatelyin front of the exit 16. An advantage of such a throttling formed as athrottling washer is that an accurate throttling can be achieved. Butthe throttling can also be formed as a contraction in the exhaust gaspipe by way of a decreased depression in one or both of the plates 12,13, or one plate can be made with a bulge which decreases the area ofthe channel, for instance the bulge 33. One reason of using a throttlingis to throttle the engine on the exhaust side to achieve decreasedexhaust emissions. Suitably the throttling is located close to theoutlet 16. Of course it would also be possible to form the throttlingdirectly in the outlet 16 or in the spark arresting screen 17. Theopenings 16 in the muffler and/or the screen holder 9 is then suitablyembodied with a smaller total size than otherwise so that they form anadditional throttling in the muffler. But a disadvantage would be thatmany users of the finished product, e.g. a chain saw, would themselvesdecrease the throttling or take it away to increase the engine output inthis way. This would increase the exhaust emissions and would bring adistinct risk of decreased cooling of the exhaust gases.

Furthermore it can be noted that the inlet hole aperture 20, which letsthe exhaust gases 21 into the converter element 5, usually has a smallerarea than the intake area of the converter element. Suitably the opening20 has a considerably smaller area than the cross section of theconverter element.

As illustrated in FIG. 1 a spark arresting screen, i.e. a structurewhich at least partly contains a wire mesh 4 or a screen 4. is locatedin the flow of exhaust gases downstream a converter element 5. As theexhaust gases are substantially heated up in the converter element 5this positioning downstream the element comes natural. Furthermore, thespark arrester screen is located in close connection to the exhaust gasoutlet 16. This is a suitable positioning since the spark arrestingscreen 3 shall protect sparks from blowing out of the exhaust gas outlet16. Should for instance a soot particle in the exhaust duct 45 upstreamthe spark arresting screen be ignited and pulled away with the flow ofexhaust gases, the spark arresting screen 3 prevents it from blowing outof the muffler. One result of the spark arresting screen beingpositioned downstream the converter element 5 is that it is subjected tovery high thermal loads. As mentioned, it is desirable that by heatingthe wire mesh it becomes self-cleansing but not self-destructive. FIG. 1shows a positioning of the spark arrester screen 3, in which it has beenclamped between the plates 12 and 13, but as mentioned also otherpositionings are possible. With the shown positioning the spark arresterscreen cannot be changed separately but the whole lid 43 alternatively50 must be changed. FIG. 2 to 8 give examples of solutions where thespark arrester screen 3 has been located on the outside of the plate 13,so that it can be possible to change the spark arrester screenseparately.

The outlet 16 in FIG. 1 consists of stamped apertures in the plate 13.The exhaust gas flow is distributed to these apertures. The whole platesurfaces between the apertures function as cooling surfaces for the wiremesh 13. Thus through this design a better cooling of the wire mesh anda longer length of life are obtained than if the wire mesh would havebeen positioned in front of one big aperture, which had functioned as anoutlet 16. Thus how the outlet is formed is of great importance. butalso the distribution of the exhaust gas flow up to the outlet and itsturbulence are very important. These conditions can favorably beinfluenced by various throttlings 33, 15, 20, 53 positioned upstream thespark arrester screen. As the spark arrester screen can be used togetherwith different types of catalytic mufflers, one or several of thesethrottlings can be used in combination to improve the working conditionsfor the spark arrester screen and also to give other design advantages.

The illustrated embodiment in FIG. 1 refers to a preferred embodimentwhere an exhaust gas duct 45 leads from the converter element 5 to theexhaust gas outlet 16.

The illustrated throttlings 33, 15, 20 and 51 can also have severalother favorable effects. One is that reduced exhaust gas emission levelsare obtained. Another one is as mentioned that the strains on the sparkarrester screen can be lowered and a third one is that a well tunedthrottling also can lead to improved noise reduction. The throttling 33contributes to distribute the exhaust gases sideways and thereby also todistribute the heat strains sideways across the spark arrester screen.Furthermore, the throttling 33 absorbs heat so that it to a certainextent reduces the heat strain on the subsequent spark arrester. Thethrottling 15 is valuable in that it creates a substantial turbulence,which distributes the flow better over the cross section of the exhaustduct 45 and thereby distributes the flow even better through the sparkarrester screen 3. The increased turbulence also results in increasedheat absorption in the exhaust duct 45. The throttling 20 upstream theconverter element creates in a similar way a substantial turbulencebefore the element 5 and results in a more even distribution of the flowover the entire cross section surface of the element. This leads partlyto a more diff-used flow after the element, and partly to a somewhatincreased conversion rate in the element. In a similar way thethrottling holes 51 create a substantial turbulence and a cooling effectof the exhaust gases 21, which is a result of the baffle 53 heating up.This is positive considering the spark arrester screen 13.

Of course the catalytic muffler 1 with a spark arrester screen 3positioned in the exhaust gas flow downstream the converter element 5can also be embodied in other ways than illustrated in FIG. 1. Forinstance, the plates 12 and 13 do not have to be joined together, butthe element 5 could be positioned in a baffle similar to the plate 12positioned with a distance to the outer plate 13. Suitably the outerwall 13 is then supplied with an exhaust gas duct corresponding to theduct 45, in which the throttlings 33 and 15 can be embodied. But theouter plate 13 does not need to have an exhaust gas duct. A furtherbaffle, for instance similar to the baffle 53, could be positionedbetween the outer plate 13 and the baffle 12. Thereby the throttlingholes 51 would create turbulence, which is favourable to the subsequentoutlet with a spark arrester screen. Also the positioning and theorientation of the converter element 5 in the muffler can vary within awide range. The muffler can also be embodied in one part, i.e. without alid.

FIG. 2 shows in cross section a solution where the spark arrester screen3 is located on the outside of the outer plate 13 or on the outside of asimilar catalytic muffler. The cooling air 10 is in this case led by acooling air duct 48 over the spark arrester screen 3. This leads partlyto a lower concentration of the exhaust gases and partly to a cooling ofthe spark arrester screen and its associated parts. For instance, in thecase of a chain saw, the amount of cooling air is about 10 times greaterthan the amount of exhaust gas and has a considerably lower temperature,approximately 100 to 150 degrees. For some catalytic mufflers a good mixand cooling can be obtained even without the cooling air duct 48. Thisis especially the case when the cooling air 10 has a suitable directionof flow even without a cooling air duct, which is consequently notnecessary, but in many cases advantageous. The same applies to theremaining preferred embodiments which are shown in FIGS. 4 to 8. In theembodiment shown in FIGS. 2 and 3 the spark arrester screen 3 consistsof a wire mesh 4 and a fastening device 6. The fastening device consistsof a folded plate, which is pressed against the wire mesh to give goodcontact and heat conduction. Of course the plate could also be joinedtogether with the wire mesh by means of stampings, gluing or soldering.The fastening device itself could also consist of an entirely cast orsoldered part onto the wire mesh. This could result in especially goodheat conduction away from the hottest parts of the wire mesh. Thefastening device 6 is supplied with at least one fastening hole 7 forscrew 7' or similar. The fastening device 6 spreads out over the centralparts of the wire mesh 4 or the screen 4 in the form of strip 8. Itcould also be realized in the form of a mesh or similar. The advantagewith these strips or meshes is that a division of the effective wiremesh area takes place. Thus the flow is forced to pass through everyopen section of the wire mesh area and the strips or similar serve asheat conductors. By this division it is always close between a wire meshaperture and a heat conducting passage 8. The fine-meshed screens thatare commonly used are normally relatively poor heat conductors. Thispartly depends on that the wire mesh itself must have thin wires or netsto limit the flow resistance and partly that the type of the materialmust be stainless and acid-proof or similar. The latter considering hightemperature tolerance and low inclination to corrode or oxidize. Thespark arrester screen 3 is here inserted in a wire mesh holder 9, whichis mounted to the muffler only along one part of its surrounding edge,here along all sides but one, so that a cleft is created on this sidenext to a pocket between the wire mesh holder and the muffler itself, sothat the spark arrester screen 3 can be inserted into this pocket. Thespark arrester screen is tightly fastened by means of a fastening screw7', which passes through the fastening hole 7 and is screwed into wall13. The wire mesh holder 9 is here embodied with a cap which hasapertures only in one direction, so that hereby the exhaust gases 21 areforced out into a desirable direction. The muffler 1 is supplied with alarge aperture 16, which exits into the pocket between the wire meshholder and the muffler. Of course, also several smaller apertures 16could be used. Thus the exhaust gases leave the muffler throughapertures 16 and through the wire mesh 4 and the wire mesh holder 9.

FIG. 4 and 5 show a somewhat different embodiment of the spark arresterscreen 3 and the screen holder 9. The apertures which are embodied inthe muffler's outer plate 13 and in the wire mesh holder 9 respectivelyhave been given a gill form. Thereby they steer the exhaust gas flow 21in a desirable direction. The fastening device 6 is in this caseembodied only along one side of the wire mesh 4 or the net 4 and it issupplied with at least one fastening hole 7 for screw 7'. This leads toa somewhat simpler spark arrester screen than according to thepreviously described embodiment. The wire mesh is inserted into the wiremesh holder in the same way, but note that only the wire mesh is goingto lie in the pocket between the wire mesh holder 9 and the muffleritself. The solution is simpler, but the heat conduction from the wiremesh will not be as effective as in the former solution. This depends onthat the passages of metal, which are spread over the wire mesh on itsin side and outside, do not get as good contact and consequently not asgood heat conduction. Even this solution is based upon that the wiremesh is divided into several effective sections to even out the heatstrain. The effective surface is approximately made as large, as in afictive case when no division is made, but in the fictive case the areasin the middle of the spark arrester screen would become very hot, whichwould lead to a considerably shorter length of life, provided that thesame type of material is used.

FIG. 6 shows a solution where a similar spark arrester screen 3 as inFIGS. 4 and 5 have been used. The wire mesh holder 9 has here beensupplied with an intake 54 for cooling air 10. This cooling air passesthrough the spark arrester screen 3 and further in a duct 55, which isarranged so that it leads into the exhaust gas duct 56, which leads theexhaust gases 21 to the exhaust gas outlet. The duct 55 exits inside theexhaust gas duct 56, so that an ejector effect is created. Cooling airand exhaust gases are mixed in a mixing chamber 57 so that itsubsequently can pass through the spark arrester screen. This embodimentis more complicated than the former ones, but leads to a dilution of theexhaust gases and consequently a reduced temperature of the mixed gaseswhen they pass through the spark arrester screen.

The embodiment according to FIGS. 7 and 8 shows a solution, in which thefine-meshed screen or the net 4 has a vaulted form, and the vaulting isturned outwards from the muffler part itself, a so called wire meshbulge 52. This wire mesh bulge can for instance be created by pressing aplane wire mesh down into a tool 41 with a suitably formed cavity. Thefastening device 6 leads around the entire circumference of the wiremesh 4, but could also have a smaller extension. Two fastening screws 7'are used to fasten the spark arrester screen 3. The fastening device 6could also improve the cooling of the spark arrester screen. Oneadvantage with the vaulted shape is that the cooling air 10 gains accessto cool the spark arrester screen in an effective way. As illustrated inthe example the wire mesh bulge 52 is unsymmetrical to create aparticularly good cooling effect. Obviously the wire mesh bulge can beembodied more or less symmetrically and in several different ways. Whenthe cooling air duct 48 is used this also serves as a cover for the wiremesh bulge 52. This is however not absolutely necessary, especially notif the fastening device 6 also leads out over the central parts of thewire mesh or the net 4.

One basic principle is that the flow dividers 8, 9, 13 are used todistribute the exhaust gas flow, so that the spark arrester screen isdivided into several effective sections, in order to even out the heatstrain. This can for instance be arranged by means of several aperturesbeing embodied in parts 13, 9 arranged upstream 13 and/or downstream 9the spark arrester screen 3. Of course, also other parts than the abovementioned ones 13, 9 can be used for this purpose.

In the described embodiment the exhaust gas outlet is located on themuffler's front side opposite the exhaust port outlet 25, but theexhaust gas outlet can obviously also be located on anyone of themuffler's remaining sides.

We claim:
 1. Muffler adapted for direct connection to a combustion engine exhaust port (2), said muffler comprising a catalytic converter element, a spark arrestor screen, and a flow divider, said spark arrestor screen (3) comprising a wire mesh (4) positioned in the exhaust gas flow downstream of said catalytic converter element (5), said flow divider comprising strips (8) fastened to the spark arrestor screen, said strips (8) being arranged upstream (13) and/or downstream (9) the spark arrester screen (3).
 2. Muffler in accordance with claim 1, wherein the spark arrester screen is positioned in close proximity to the exhaust gas outlet (16).
 3. Muffler in accordance with claim 1, wherein the wire mesh has a fastening device (6), said fastening device consisting of a folded plate which is secured to the wire mesh (4) and which, in turn, has at least one fastening hole (7) for receipt of a mechanical fastener (7).
 4. Muffler in accordance with claim 3, wherein the fastening device (6) is arranged along one side of the wire mesh (4).
 5. Muffler in accordance with claim 3, wherein the fastening device (6) surrounds the entire circumference of the wire mesh (4).
 6. Muffler in accordance with claim 5, wherein a portion of the fastening device (6) extends out over central parts of the wire mesh (4), said portion being formed as strips (8).
 7. Muffler in accordance with claim 3, further comprising a wire mesh holder (9), said wire mesh holder having a peripheral edge and being mounted to the muffler along only a portion of said peripheral edge to form an aperture next to a pocket defined between the wire mesh holder (9) and the muffler, said spark arrester screen (3) being adapted for insertion into said Pocket via said aperture, and the muffler and wire mesh holder (9) define a plurality of exhaust apertures (16), which communicate with the pocket such that the exhaust gases leave the muffler through said exhaust apertures (16) and through the wire mesh (4).
 8. Muffler in accordance with claim 7, wherein at least some of said exhaust apertures are shaped and adapted to direct the exhaust gas flow sideways.
 9. Muffler in accordance with claim 7, wherein the wire mesh (4) has a vaulted form, and that the vaulting is turned outwards from the muffler part to form a wire mesh bulge (52).
 10. Muffler in accordance with claim 7, wherein at least one additional throttling (15, 33, 20, 51) is provided in the muffler (1) through which exhaust gas flow must pass before leaving the muffler.
 11. Muffler in accordance with claim 10, wherein at least some of the exhaust apertures (16) have a small size and provide said at least one additional throttling.
 12. Muffler in accordance with claim 10, wherein said at least one additional throttling (20) is provided immediately upstream the catalytic converter element (5) by means of an aperture, said aperture having a considerably smaller area than the converter element cross-sectional area and being located in a converter element enclosure.
 13. Muffler in accordance with claim 10, wherein said at least one additional throttling comprises a plurality of throttling holes (51) in a baffle (53), said baffle being disposed upstream the converter element (5) in a demarcation, said demarcation dividing the muffler volume between the element (5) and the exhaust port (2).
 14. Muffler in accordance with claim 10, wherein a main additional throttling effect is achieved by a plurality of throttling washers disposed downstream of the converter element.
 15. Muffler in accordance with claim 14, wherein said at least one additional throttling is located immediately upstream of the spark arrester screen, said additional throttling being provided by a throttling washer (15). 